How can I stop DELL 660 PC from freezing with no obvious reasons why its doing it?

Does the computer completely hangs? or just the mouse?

Have you checked HDD's health?

Check to see if the vents are clogged with dust (hairballs). Also, yes, I would recommend updating the video and network drivers to begin.

The most usual cause is CPU overheating.  So check the heat exchanger is clean of dust  and the CPU heatsink fan is spinning.

Run a memory test as this could be a cause as well.

Hard drive failures are possible but generally different symptoms.

What is a Dell 660? Latitude? Inspiron? Poweredge...? Desktop? Laptop? Please tell us the proper model number.

Have you tested the RAM using memtest86+? The HD using the disk manufacturer's diagnostic utility? You'll find those tools on the UBCD:

http://mirror.sysadminguide.net/ubcd/ubcd535.iso

Clean out all dust. Make sure all the fans run smoothly. check the Heatsink is properly attached.

Do a fresh OS installation. That should always be done on a system you get 2nd hand.

I would start with the power supply unit and RAM.
They are the most inexpensive components to replace and will also not require any reconfiguration of the existing software to swap out.
Do you have some known good RAM and a PSU you can test with (even if it's just to confirm the fault and before ordering a replacement whatever).

After that, it's most likely to be a bad hard disk drive.
To replace this, you'll have to do a full operating system reinstall (or clone the failing drive using your favorite cloning utility).

OK. Thank you all. this is a Dell inspiron very basic model.   I have not done any repair work in years and I messed up.  It is 5-6 YO and really not that dusty but I blew out what was there. It was running cool.  As I said in original question PC was cool and fast except when it decided to freeze.  I did everything that you all Said  memtest, etc.  Everything.  Even the power supply. I have a little tester I used. I guess I remembered the basics. HERE IS WHAT I DID:  I did all the hardware tests except the HD and video. wanted to try other options before I tried to update drivers.  So All tested good?  Next. I tried to make a recovery disk with no joy. PC would not let me.  Then I tried  to do a system restore  and it kept spinning and spinning,  so i thought the same as most of you... its The HDD.  I got impatient and tried to restart in Mid Sys Restore after 45 minutes of spinning... error message said it Could not find the system 32folder and to insert a recovery disk. I have seen that message a1000 times but do not know what to do now. PC will not boot because that file is missing.  I have a generic win 8.1 disk at home and will try that next. I do not have the space or extra PCs to test the HD anymore, so this is my plan try to find sys 32 ON UBCD, then try my generic 8.1 disk. If not I will replace the Sata drive that I have in my closet and try to reinstall OS. HD just pops out so it is not a big deal. Could be the Sata cable.  I dont know.  You guys taught me all that I know about computer repair, but I quit at windows 7 and know just a little about 8.1.

So Part II of this is why would System Restore get hung up? I have never seen that happen before. I was embarrassed because the guy was looking over my shoulder. will update you tomorrow. Will burn a new UBCD in AM

Don't bother with Windows 8. download a Windows 10 iso, create a DVD or bootable USB stick from it, then just install s 10. As long as you install the correct version corresponding to the Windows 8 version the PC originally came with (Windows 10 home or Pro), it will activate and register with the m$ servers automatically as soon as it has an internet connection. It'll use the product key embedded in the BIOS. If you do get asked for a product key during the installation, just click on "I don't have a key". You still have the free upgrade to Windows 10 available for 1 month, and it is definitely the better OS when compared to 8, so you should take advantage of the free upgrade offer.

Hi Donnie, you posted >>   I tried to make a recovery disk with no joy. PC would not let me.  <<  what happened?  any errors, or messages?

since you ASSume the pc is fine, you could do a clean boot and see if things are better then, here is how :
https://support.microsoft.com/en-us/kb/929135

Thanks Guys.
1. I stupidly  stopped a Sys Restore  midstream after 45 minutes and when I tried to restart ERROR was
"You need to repair your computer System is missing the system/System 32 folder"  

So I have no access at all. Before this I could not even get into "Safe mode"  anyway It was not recognizing F8 and just went to normal start-up.

I have to try to get in and work with A New updated WIN PE CD or  new UBCD CD which I just made (Bootable...didn't forget that and hope I remember what to do..Probably wont.  Been A long time.

I made a portable bootable USB flash drive for Windows 10 with rufus. Never booted with a flash drive. I still use CDs. Old guy.

So I am off with my  Bootable items and hopefully I will find out what is wrong. I may just sell the guy a 6 yo WD Sata drive, format & update from win 8.1 to Windows 10, as my last option.  I have made both a bootable DVD and a USB Flasher. I certainly cannot do any more harm than i already have done. So here goes. I cannot contact EE on my phone about this issue. Guy has horrible service at his house.  

Following is what I have to deal with. The guy is so computer illiterate He does NOT know what a browser is, what a flash drive is, how to drag and drop something, what COA is, what Windows version he has, and on and on. But he surely knows this...A porn site that froze before he could get rid of it before I saw it. I actually think he has a sneaky piece of malware that evolves when I get close in the registry. We shall see. Blind leading the blind...So again you all have been invaluable to me helping me make maybe  $250K in 7 years. EE members actually repaired 100's of PCs for me. All I did was what you all told me to do, screw by screw.

I will update you all tomorrow. I really appreciate your help ALL OF YOU.  It has been a year or so and 2 responders are faithful guys that have helped me a couple of Dozen times each over the years.  One of you knows who you are, I wont name you because I dont want to offend anyone else  but I WILL SAY THIS... Every responder to this question has given me something this time that is usable. All of you did.  So after 20 mos, 2 of 7 rezsponders are guys that have helped me immensely in the past. How amazing is that?

 Please dont quit me if I dont respond quickly. I know NOTHING about windows 10 or how to install it so it is going to take a while unless I get lucky. And from a flash drive too? I just cant imagine. But Im on my way. I also have a bit of alzhiemers so I dont remember what I learned about computing the next day. Here we go.  Talking too much again.

 I have notes from every contributer and will combine what i need to repair this antique.  I WILL do it.

Regards,
Donnie

Okay keep us posted

>>   I know NOTHING about windows 10   <<  nobody does really, since it's new- except for some nerds , following windows at every pace. So you're not alone!

that said, you'll have to restart the restore - or try downloading a repair disk

I was able to boot into the PC with My 2015 WIN PE Generic Rescue disk,  IT is really a good one. But I am lost. technology is too far ahead of me.  I tried many options. But I was turned away from success. BTW, HDD passed all deep tests.

MAIN PROBLEM:  I am missing the System32  "CMD.EXE"  file. and it could not boot. I don't know how to find a copy and how to get it onto this dell.  I made a Repair disk for this guy years ago but he has nothing...no CD, no prod key, no paperwork, NOTHING!  Just the service tag. period.

My Win 10 dvd and Flash drive are only good for fresh installs not upgrades and this is definitely an upgrade in the Windows sytems's eyes. They are only good for a brand new build. Changing & formatting HDD will do no good either because of the OS info on MB and in BIOS. I can pay for a recovery disk from Dell, but guy did not like that idea. This win10 thing seems not to work on any system but the one it was designated for.

SO ANYWAY...How/where can I get a Win 10 OS that will boot and install on this Dell Inspiron 660. Is there a generic 8.1 or 10 disk or flasher that I can use to reinstall this without MS or DEll's interference?

So you are looking for an original DELL OEM Windows 7 Install DVD?

Or an original DELL OEM Windows 8 Install DVD?

Please verify.

rindi: Will make that copy because Win 10 did not work. to upgrade this dell from 8.1 to 10
efrimpol:  Windows 8.1 Dell 660 inspiron
NOBUS:Ok thanks to all. I am able to enter uefi with  F12 (i think) or My Win PE dvd.  Disable secure boot, yes? Then what? Install win 10 or win 8.1
I have a new build of a Dell repair disk from Dell's own site. made iso, then made bootable CD. from iso. Starting to remember things now. hope it works. My very good win pe disc has Paragon, Ghost, Easus, , total of 9 different repair apps. All newer tech than I am used to. Worked my way around a bit yesterday but still missing that System\system32\cmd.exe file to boot.  Going to make the win 10 disk at MS but first will try my Dell specific repair and recovery disk. and before that, I will disable secure boot. Thats the plan for now.

Will update you after I try these one at a time.

While in uefi, I tried to do sys restore comd  but it just did not work. I am inputting rstrui.exe in cmd line but it is not reading the command.

Thanks for all your help.  funny how two of you have been here for me for ten years at least. And still helping this old man, but you guys are 10 years older also good nite, Donnie

>>  Disable secure boot, yes? Then what?  <<  this is neded to make it possible to boot from other systems and devices than the OS

>>   but still missing that System\system32\cmd.exe file to boot  <<  you don't need any file to boot; you need a working bios, set to the proper boot priority.
When that device is adressed after boot it will start to load the OS

why do you want that file?  what do you want to do when you have it?

I think I disabled that already. I was finally able to boot into CDs & dvd's the last couple of times. Just did not remember what to do once I got in with UBCD , Win PE, etc. Been away too long.

About that file....I was just telling you what the error message said...that it cannot boot because that file is missing.. Have not been there in 2 days.  secure boot is diabled I believe, as suggested. Will try again. In meantime I bought a OS recovery Disk for this guy from Dell. On its way. But I always do as you say first. I am busy for couple of days so be back maybe thursday
Thanks, old friend.

>>  I think I disabled that already  <<   fine, but if you forget easily, best make a note of the steps taken
i'll be 'round donnie, so  take your time

Sfter i spent the money for a boot flash drive, Dell tech support said this pc was not eligible/did not qualify for a win 10 upgrade.  So I got it running with your input and fixed but they forced the guy to buy a new PC with Win 10 installed before i could ask you guys.. it runs and i am its new owner. Guy says it still freezes but not as much Going to help guy set it up NOW> Will be back with new questions if i have any. Closing this for now. Gling to be a trip with my 1st look at win  10. Thanks to ALL of you, but 2 did assist to help get it going again when iit was stone cold dead.
Thanks to all.
Donnie.

Thanks again to all. I used a bit of info from all.

did you forget to close this Q Donnie?

U2 guys helped the most since it really is a Windows 10 issue now. I thought I close this question on my computer yesterday. I know I did.this is from my phone so it should be closed now but you can bet I will be back I am going to have to do windows 10 update on my personal computers I got a little peek at Windows 10 when I set the guys computer up yesterday. It resembles Windows 7 but I will need help. I didn't even know how to close this question. I am a beginner again. Thank you both once more have a good day

i know what you mean Donnie, i had problems with the new closing system also, and many others
i wonder why they make it so difficult - when it was so easy before...